The present invention relates to internal combustion engines and, more particularly, to an improved method and apparatus for preventing oil leakage into a cylinder of an engine by oil flow along a stem of an engine valve.
Internal combustion engines and, in particular, diesel engines of the type used in diesel-electric propulsion systems, utilize overhead valve systems in which lubricating oil is pumped to a location above the valves from whence it flows by gravity back to an oil sump. The oil is pumped through hollow valve push rods to rocker arms which are connected in driving relationship to valve tappet assemblies that operate the valves. The valve tappet assemblies include means for carrying oil from the rocker arms to their interfaces with the valves. The valve tappet assembly includes a tappet foot seated on an end of the valve stem, which foot includes a bottom aperture that allows oil to pass through and lubricate the contact surface between the tappet foot and valve stem end. The tappet foot upper surface is cup-shaped for receiving a tappet ball end of a tappet shank and allows excess oil to overflow and spill onto the area at the end of the valve.
During low speed operation of the engine, particularly when the engine is allowed to idle, pressure in the cylinder drops to a low value, tending to draw oil into the cylinder along the valve stem through the valve guide. Such oil accumulates in the cylinder and the intake manifold in a partially burned condition. When the engine is subsequently brought up to a running speed, the unburned combustion products, a mixture of oil and soot, is discharged from the engine and sprayed into the air where it rapidly precipitates out onto the locomotive and surrounding surfaces. Incomplete combustion of this oil material also results in undesirable smoking of the engine.
Heretofore it has been the practice to attempt to prevent oil from leaking into diesel engine cylinders through engine valves by installing an umbrella-like device about the valve stem between the valve spring retainer and the valve guide. This device fits snugly about the valve stem and prevents oil from running down the valve stem into the valve guide. The device is shaped as an annular ring having a sloped or chamfered outer circumferential perimeter. In essence, the oil is diverted outward from the valve stem over the outer perimeter of the device and away from the valve stem. While this device is generally effective, it has the disadvantage of being difficult to access for either installation or repair since it is located below a valve keeper and within a valve spring. Accordingly, it would be desirable to provide a method and apparatus for deflecting oil from the valve stem but without the servicing difficulties of the prior art.